There has hitherto existed a printed board in which a circuit composed of a copper foil is formed on a substrate by photolithography. Photolithography includes the step of etching a copper foil and high costs are required for a treatment of waste fluid generated by etching.
There has been known, as the technology requiring no etching, a method in which a conductive film is formed on a substrate using a copper particulate dispersion (copper ink) containing copper particulates (copper nanoparticles) dispersed in a dispersion vehicle (see, for example, Patent Literature 1). According to this method, a film of the copper particulate dispersion is formed on the substrate and, after drying the film, copper particulates in the film are melted by exposure to light and thus conductivity is imparted to the film.
In such a copper particulate dispersion, there have been known some specific examples of the formulation in which copper particulates are dispersed. However, there has never been known general formulation in which copper particulates are dispersed.
During storage before use of the copper particulate dispersion, copper particulates in a dispersion vehicle may be sometimes aggregated to form a precipitate (caking) with the lapse of time, and thus it has been required to improve dispersion stability.